Method for removing genes encoding antibiotic resistance

ABSTRACT

A method for removing antibiotic resistance genes (ARGs). The method includes the following steps: 1) coagulation and sedimentation of waste water; 2) biochemical treatment; 3) disinfection by peracetic acid; 4) sterilization by high pressure CO 2 ; 5) photocatalysis by nano-titanium dioxide (TiO 2 ); and 6) depositing.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. §119 and the Paris Convention Treaty, thisapplication claims the benefit of Chinese Patent Application No.201210086161.8 filed Mar. 29, 2012, the contents of which areincorporated herein by reference. Inquiries from the public toapplicants or assignees concerning this document or the relatedapplications should be directed to: Matthias Scholl P.C., Attn.: Dr.Matthias Scholl Esq., 14781 Memorial Drive, Suite 1319, Houston, Tex.77079.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for removing antibiotic resistancegenes (ARGs) from wastewater.

2. Description of the Related Art

Extensive use or abuse of antibiotics has resulted in more and moreserious problems of environmental pollution. Selective pressure imposedby the antibiotics is capable of inducing animal microorganisms orenvironmental microorganisms to produce antibiotic resistance genes(ARGs), which seriously threatens ecological environmental security andhuman health. ARGs are capable of horizontally transferring among florasof the same or different species via plasmid, integration-genecassette,transposon, and other mobile genetic elements. Characterized inpersistence and replicability in the environment, ARGs have beenconsidered to be a new type of environmental pollutants.

A waste water treatment system is a main way for the antibioticresistance genes to enter the water environment. The antibioticresistance genes enter the water environment via medical waste water,pharmaceutical waste water, farm sewage, and domestic sewage. Because aconventional waste water treatment technology has no obvious effect inremoving many antibiotics and antibiotic resistance genes, the treatedwater still contains a considerable number of resistance genes.

Outlet water from the waste water treatment plant and sludge applied tosoil are considered to be important resources of antibiotic resistancegenes distributed in the surface water, soil water, and groundwater. Theuse of ARGs molecular tags for tracing the source of the antibioticresistance genes has proved that resistance genes of antibioticsrelevant to human diseases are mainly from waste water treatment plantsrather than nearby livestock farms or upper rivers. Thus, the removal ofthe resistance genes or resistant bacteria can be realized by focusingon safe recovery of the waste water; and the sterilization of the wastewater is a necessary process for improving the safety and quality of thewater.

SUMMARY OF THE INVENTION

In view of the above-described problems, it is one objective of theinvention to provide a method for removing antibiotic resistance genes(ARGs). The method of the invention is capable of effectively removingantibiotic resistance genes, and provides technical support for advancedwaste water treatment, and improves the safety and quality of the water.

To achieve the above objective, in accordance with one embodiment of theinvention, there is provided method for removing antibiotic resistancegenes (ARGs), the method comprising the following steps:

1) Coagulation and Sedimentation

-   -   introducing waste water into a coagulation and sedimentation        tank; coagulating and depositing the waste water using        polyaluminumchloride (PAC) as a flocculate and polyacrylamide        (PAM) as a coagulant, a dosage of the flocculate being 3-5 mg        per liter of the waste water, and a dosage of the coagulant        being 1-3 mg per liter of the waste water; and introducing a        supernatant after deposition into a sand filter for further        lowering a water turbidity;

2) Biochemical Treatment

-   -   conducting an anaerobic-anoxic-oxic (A²/O) activated sludge        process to remove nitrogen and phosphorus from the waste water        after sand filtering in step 1) and to lower a chemical oxygen        demand (COD); and introducing the water into a secondary        sedimentation tank for slurry separation;

3) Disinfection by Peracetic Acid

-   -   pumping the waste water after the biochemical treatment from the        secondary sedimentation tank into a sterilization tower; and        disinfecting the water using peracetic acid for 10 min, a dosage        of peracetic acid being 80-100 mg/L;    -   a preparation of peracetic acid comprising the following steps:        inputting glacial acetic acid into a barrel, mixing glacial        acetic acid with 2% of sulfuric acid; adding 30% of hydrogen        peroxide, a dosage ratio between hydrogen peroxide and glacial        acetic acid being 1:2, and adding 1 g/L of phosphoric acid        having a concentration of 0.1% as a stabilizer to form peracetic        acid; and preserving peracetic acid at a room temperature for 2        days;

4) Sterilization by High Pressure CO₂

-   -   injecting CO₂ gas having a pressure of 0.5-1.5 mPa into the        sterilization tower, and maintaining the high pressure CO₂to        sterilize for 5-10 min, the CO₂ gas being output from a high        pressure CO₂ cylinder, passing through a pressure reducing valve        and a high pressure pipeline, and finally into the sterilization        tower from microporous aeration tubes arranged at a bottom of        the sterilization tower;

5) Photocatalysis by Nano-titanium Dioxide (TiO₂)

-   -   introducing the water after the sterilization into a        nano-TiO₂photocatalytic oxidation pool; the photocatalytic        oxidation pool being provided with a spherical nano-TiO₂        suspension filler comprising a nuclear body and a coating; a        nano-TiO₂ coating being coated on the nuclear body; the nuclear        body being made of a polyethylene material by one step injection        molding; a radius of the nuclear body being between 3 and10 cm;        the coating being formed by dip coating TiO₂ powder having a        grain size of not exceeding 100 nm; a thickness of the coating        being between0.05 and 0.45 mm; and a gravity of the spherical        nano-TiO₂ suspension filler being 95-99.8% of a gravity of        water;    -   meanwhile, tilting a plurality of three-layered nano-TiO₂ meshes        for 30° in the sedimentation tank to oxidize, decompose,        degrade, and remove resistant genes from the waste water under        daylight or ultraviolet irradiation; and    -   the nano-TiO₂ mesh being formed by coating a layer of nano-TiO₂        onto a stainless steel mesh; and

6) Depositing the Water for 1 h After Step 5), Finely Filtering theWater to Remove Impurities.

In a class of this embodiment, the flocculant in step 1) is a polymericferric sulfuric solution. The coagulant is a mixture of a poly diallyldimethyl ammonium chloride, a polyaluminum chloride, aluminum sulfate,and ferric chloride having a ratio of 3:2:1:1. A dosage of the coagulantis 20-150 mg/L.

In a class of this embodiment, the nuclear body of the sphericalnano-TiO₂ suspension filler is in a shape of an ellipsoid, a hollowsphere, a cube, and a cuboid.

Advantages of the invention are summarized as follows:

The method meets demands of advanced waste water treatment, water reuse,economic promotion, and social and environmental sustainability. Themethod focuses on toxic pollutants-antibiotic resistance genes andpathogenic microorganisms in wastewater treatment; uses a combination ofadvanced technologies, and employs carbon dioxide sterilizationtechnology in the waste water treatment. Thus, the method effectivelyremoves resistant genes, and provides technical support for advancedwaste water treatment and the safety and quality of the water.

DETAILED DESCRIPTION OF THE EMBODIMENTS

For further illustrating the invention, experiments detailing a methodfor removing antibiotic resistance genes (ARGs) are described below. Itshould be noted that the following examples are intended to describe andnot to limit the invention.

Example 1

A method for removing antibiotic resistance genes (ARGs), comprises thefollowing steps:

1) Coagulation and Sedimentation

-   -   Introduce waste water into a coagulation and sedimentation tank,        coagulate and deposit the waste water by using a flocculate PAC        and a coagulant PAM. A dosage of the flocculate PAC is5 mg per        liter of the waste water, and a dosage of the coagulant PAM is3        mg per liter of the waste water. Introduce a supernatant after        deposition into a sand filter to further lower a water        turbidity.

2) Biochemical Treatment

-   -   Conduct an anaerobic-anoxic-oxic (A²/O) activated sludge process        to remove nitrogen and phosphorus from the water after sand        filtering in step 1) and to lower a chemical oxygen demand        (COD); and introduce the water into a secondary sedimentation        tank for slurry separation.

3) Disinfection by Peracetic Acid

-   -   Pump the water after the biochemical treatment from the        secondary sedimentation tank into a sterilization tower;        disinfect the water by using peracetic acid for 10 min. A dosage        of peracetic acid is 100 mg/L.    -   The preparation of peracetic acid comprises the following steps:        input glacial acetic acid into a barrel; mix glacial acetic acid        with 2% sulfuric acid; add 30% hydrogen peroxide (a dosage ratio        between hydrogen peroxide and glacial acetic acid is 1:2), and        add 1 g/L of phosphoric acid having a concentration of 0.1% as a        stabilizer to form peracetic acid; and preserve peracetic acid        at a room temperature for 2 days.

4) Sterilization by High Pressure CO₂

-   -   Inject CO₂ gas having a pressure of 1.5 mPa into the        sterilization tower in step 3). The CO₂ gas is output from a        high pressure CO₂ cylinder, passes through a pressure reducing        valve and a high pressure pipeline, and finally into the        sterilization tower from microporous aeration tubes arranged at        a bottom of the sterilization tower. Distribute the CO₂ gas in        the water for sterilization; and maintain a time of the high        pressure CO₂ sterilization for 10 min.

5)Photocatalysis by Nano-titanium Dioxide (TiO ₂)

-   -   Introduce the water after the high pressure CO₂ sterilization        into a nano-TiO₂photocatalytic oxidation pool. The        photocatalytic oxidation pool is provided with a spherical        nano-TiO₂ suspension filler comprising a nuclear body and a        coating. A layer of nano-TiO₂is coated on the nuclear body. The        nuclear body is made of a polyethylene material by one step        injection molding. A radius of the nuclear body is 3-10 cm. The        coating is formed by dip coating TiO₂ powder having a grain size        of no exceeding 100 nm. A thickness of the coating is 0.05-0.45        mm A specific gravity of the spherical nano-TiO₂ suspension        filler is 95-99.8% of a specific gravity of water.

The surface of the spherical nano-TiO₂ suspension filler is coated withthe layer of the nano-TiO₂. TiO₂ belongs to an N-type semiconductor.According to a theory of photocatalysis:the N-type semiconductormaterial has discontinuous energy bands, that is, a forbidden bandexists between a valence band and a conduction band. When oxidesemiconductor particles are irradiated by photons having energy largerthan a width of the forbidden band, electrons jump from the valence bandto the conduction band, thereby producing electron-hole pairs. Theelectrons have reducibility, and the holes have oxidation. The holes arein contact with OH⁻ arranged on a surface of the oxide semiconductorparticle and produce OH free radical shaving a strong oxidation. Theactive OH free radicals oxidize many refractory organic matters intoinorganic matters, such as CO₂ and H₂O.

Chemical equation is summarized as follows:

TiO₂→e+h′

h′+H₂O→.O⁻ ₂

.O⁻ ₂++H′→H₂O.

2H₂O.→O₂+H₂O₂

H₂O₂+.O⁻ ₂→HO.+OH⁻+O₂   (1)

Meanwhile, tilt a plurality of three-layered nano-TiO₂ meshes for 30° inthe sedimentation tank to oxidize, decompose, degrade, and removeresistant genes from the waste water under the day light, ultravioletirradiation of cloudy day and a time after the sunset.

-   -   The nano-TiO₂ mesh is formed by coating a layer of nano-TiO₂        onto a stainless steel mesh.

6) Deposit the Water for 1 h After Step 5), Finely Filter the Water toRemove Remaining Impurities.

The flocculant in step 1) is a polymeric ferric sulfuric solution. Thecoagulant is a mixture of a poly diallyl dimethyl ammonium chloride, apolyaluminum chloride, aluminum sulfate, and ferric chloride having aratio of 3:2:1:1.

AI-type integron (incl 1), a sulfa resistance gene (sul I, sul II, sulIII), and a tetracycline resistance gene (tet A, tet M, tet W, tet Q) inan outlet water are shown in Table 1:

TABLE 1 intI 1 sul I sul II sul III tet A tet M tet M tet W Inlet waterquality 7.5 × 10⁸ 3.6 × 10⁹ 4.2 × 10⁷ 5.4 × 10⁷ 5.1 × 10⁵ 2.2 × 10⁴ 8.9× 10⁷ 3.4 × 10⁵ index(copies/ml) Killing rate/lg 7.75 8.64 6.87 6.524.99 4.00 6.87 4.32

Example 2

A method for removing antibiotic resistance genes (ARGs), comprising thefollowing steps:

1) Coagulation and Sedimentation

-   -   Introduce waste water into a coagulation and sedimentation tank,        coagulate and deposit the waste water by using a flocculate PAC        and a coagulant PAM. A dosage of the flocculate PAC is 3 mg per        liter of the waste water, and a dosage of the coagulant PAM is 1        mg per liter of the waste water. Introduce a supernatant after        deposition into a sand filter to further lower a water        turbidity.

2) Biochemical Treatment

-   -   Conduct an anaerobic-anoxic-oxic (A²/O) activated sludge process        to remove nitrogen and phosphorus from the water after sand        filtering in step 1) and to lower a chemical oxygen demand        (COD); and introduce the water into a secondary sedimentation        tank for slurry separation.

3) Disinfection by Peracetic Acid

-   -   Pump the water after the biochemical treatment from the        secondary sedimentation tank into a sterilization tower;        disinfect the water by using peracetic acid for 10 min. A dosage        of peracetic acid is 80 mg/L.    -   A preparation of peracetic acid comprises the following steps:        input glacial acetic acid into a barrel; mix glacial acetic acid        with 2% sulfuric acid; add 30% hydrogen peroxide (a dosage ratio        between hydrogen peroxide and glacial acetic acid is 1:2), and        add 1 g/L of phosphoric acid having a concentration of 0.1% as a        stabilizer to form peracetic acid; and preserve peracetic acid        at a room temperature for 2 days.

4) Sterilization by High Pressure CO₂

-   -   Inject CO₂ gas having a pressure of 0.5-1.5 mPa into the        sterilization tower in step 3). The CO₂ gas is output from a        high pressure CO₂ cylinder, passes through a pressure reducing        valve and a high pressure pipeline, and finally into the        sterilization tower from microporous aeration tubes arranged at        a bottom of the sterilization tower. Distribute the CO₂ gas in        the water for sterilization; and maintain a time of the high        pressure CO₂ sterilization for 5 min.

5) Photocatalysis by Nano-titanium Dioxide (TiO₂)

-   -   Introduce the water after the high pressure CO₂ sterilization        into a nano-TiO₂photocatalytic oxidation pool. The        photocatalytic oxidation pool is provided with a spherical        nano-TiO₂ suspension filler comprising a nuclear body and a        coating. A layer of nano-TiO₂ is coated on the nuclear body. The        nuclear body is made of a polyethylene material by one step        injection molding. A radius of the nuclear body is 3-10 cm. The        coating is formed by dip coating TiO₂ powder having a grain size        of no exceeding 100 nm A thickness of the coating is 0.05-0.45        mm A specific gravity of the spherical nano-TiO₂ suspension        filler is 95-99.8% of a specific gravity of water.    -   The surface of the spherical nano-TiO₂ suspension filler is        coated with the layer of the nano-TiO₂. TiO₂ belongs to an        N-type semiconductor. According to a theory of photocatalysis:        the N-type semiconductor material has discontinuous energy        bands, that is, a forbidden band exists between a valence band        and a conduction band. When oxide semiconductor particles are        irradiated by photons having energy larger than a width of the        forbidden band, electrons jump from the valence band to the        conduction band, thereby producing electron-hole pairs. The        electrons have reducibility, and the holes have oxidation. The        holes are in contact with OH⁻ arranged on a surface of the oxide        semiconductor particle and produce OH free radicals having a        strong oxidation. The active OH free radicals oxidize many        refractory organic matters into inorganic matters, such as CO₂        and H₂O.

Chemical equation is summarized as follows:

TiO₂→e+h′

h′+H₂O→.O⁻ ₂

.O⁻ ₂++H′→H₂O.

2H₂O.→O₂+H₂O₂

H₂O₂+.O⁻ ₂→HO.+OH⁻+O₂   (1)

-   -   Meanwhile, tilt a plurality of three-layered nano-TiO₂ meshes        for 30° in the sedimentation tank to oxidize, decompose,        degrade, and remove resistant genes from the waste water under        the day light, ultraviolet irradiation of cloudy day and a time        after the sunset.    -   The nano-TiO₂ mesh is formed by coating a layer of nano-TiO₂        onto a stainless steel mesh.

6) Deposit the Water for 1 h After Step 5), Finely Filter the Water toRemove Remaining Impurities.

The flocculant in step 1) is a polymeric ferric sulfuric solution. Thecoagulant is a mixture of a poly diallyl dimethyl ammonium chloride, apolyaluminum chloride, aluminum sulfate, and ferric chloride having aratio of 3:2:1:1. A dosage of the coagulant is 20-150 mg/L.

A I-type integron (incl 1), a sulfa resistance gene (sul I, sul II, sulIII), and a tetracycline resistance gene (tet A, tet M, tet W, tet Q) inan outlet water are shown in Table 2:

TABLE 2 intI 1 sul I sul II sul III tet A tet M tet M tet W Inlet waterquality 3.3 × 10⁵ 3.2 × 10⁶ 5.6 × 10⁶ 1.9 × 10³ 2.1 × 10⁴ 6.9 × 10⁴ 6.3× 10⁴ 5.4 × 10² index(copies/ml) Killing rate/lg 4.75 5.94 5.86 2.723.99 3.95 3.87 1.99

Preferably, add an adsorption column comprising an adsorbent as an endof the biochemical treatment in step 2) to adsorb soluble microbialproducts (SMP) in the water to be treated; and steps 3)-6) are followeduntil the recovered water is obtained.

The adsorbent is a nano-superfine powder adsorbent. The nanometersuperfine powder adsorbent is prepared by using the followingingredients: 10-25 weight parts of a trimethylsilyl cagepolysilsesquioxane, 5-10 weight parts of a nano-active carbon powder,5-10 weight parts of a nano-diatomaceous earth, 18-28 weight parts of aactive clay. The above ingredients are mixed at a room temperature toform the nano-superfine powder adsorbent.

While particular embodiments of the invention have been shown anddescribed, it will be obvious to those skilled in the art that changesand modifications may be made without departing from the invention inits broader aspects, and therefore, the aim in the appended claims is tocover all such changes and modifications as fall within the true spiritand scope of the invention.

The invention claimed is:
 1. A method for removing antibiotic resistancegenes (ARGs), the method comprising the following steps: 1) Coagulationand Sedimentation  introducing waste water into a coagulation andsedimentation tank; coagulating and depositing the waste water usingpolyaluminumchloride (PAC) as a flocculate and polyacrylamide (PAM) as acoagulant, a dosage of the flocculate being 3-5 mg per liter of thewaste water, and a dosage of the coagulant being 1-3 mg per liter of thewaste water; and introducing a supernatant after deposition into a sandfilter for further lowering a water turbidity; 2) Biochemical Treatment conducting an anaerobic-anoxic-oxic (A²/O) activated sludge process toremove nitrogen and phosphorus from the waste water after sand filteringin step 1) and to lower a chemical oxygen demand (COD); and introducingthe water into a secondary sedimentation tank for slurry separation; 3)Disinfection by Peracetic Acid  pumping the waste water after thebiochemical treatment from the secondary sedimentation tank into asterilization tower; and disinfecting the water using peracetic acid for10 min, a dosage of peracetic acid being 80-100 mg/L, and a preparationof peracetic acid comprising the following steps: inputting glacialacetic acid into a barrel, mixing glacial acetic acid with 2% ofsulfuric acid; adding 30% of hydrogen peroxide, a dosage ratio betweenhydrogen peroxide and glacial acetic acid being 1:2, and adding 1 g/L ofphosphoric acid having a concentration of 0.1% as a stabilizer to formperacetic acid; and preserving peracetic acid at a room temperature for2 days; 4) Sterilization by High Pressure CO₂  injecting CO₂ gas havinga pressure of 0.5-1.5 mPainto the sterilization tower, and maintainingthe high pressure CO₂to sterilize for 5-10 min, the CO₂ gas being outputfrom a high pressure CO₂ cylinder, passing through a pressure reducingvalve and a high pressure pipeline, and finally into the sterilizationtower from microporous aeration tubes arranged at a bottom of thesterilization tower; 5) Photocatalysis by Nano-titanium Dioxide (TiO₂) introducing the water after the sterilization into a nano-TiO₂photocatalytic oxidation pool, and tilting a plurality of three-layerednano-TiO₂ meshes for 30° in the sedimentation tank to oxidize,decompose, degrade, and remove resistant genes from the waste waterunder daylight or ultraviolet irradiation, the photocatalytic oxidationpool being provided with a spherical nano-TiO₂ suspension fillercomprising a nuclear body and a coating; a nano-TiO₂ coating beingcoated on the nuclear body; the nuclear body being made of apolyethylene material by one step injection molding; a radius of thenuclear body being between 3 and10 cm; the coating being formed by dipcoating TiO₂ powder having a grain size of not exceeding 100 nm; athickness of the coating being between0.05 and 0.45 mm; and a gravity ofthe spherical nano-TiO₂ suspension filler being 95-99.8% of a gravity ofwater; and the nano-TiO₂ mesh being formed by coating a layer ofnano-TiO₂ onto a stainless steel mesh; and 6) Depositing the Water for 1h After Step 5), Finely Filtering the Water to Remove Impurities.
 2. Themethod of claim 1, wherein the flocculant in step 1) is a polymericferric sulfuric solution; the coagulant is a mixture of a poly diallyldimethyl ammonium chloride, a polyaluminum chloride, aluminum sulfate,and ferric chloride having a ratio of 3:2:1:1; and a dosage of thecoagulant is 20-150 mg/L.
 3. The method of claim 1, wherein the nuclearbody of the spherical nano-TiO₂ suspension filler is in the shape of anellipsoid, a hollow sphere, a cube, and a cuboid.